Variable-speed motor.



No. 775.810. I PATENTED NOV. 22,1904. M. PFATISCHER.

VARIABLE SPEED MOTOR.

APPLICATION FILED APR. 7, 1904.

N0 MODEL. SSHBETS-SHEET 1.

No. 775,310. PATENTED NOV. 22, 1904.. M. PFATISGHER.

VARIABLE SPEED MOTOR.

APPLICATION FILED APR. 7, 1904.

N0 MODEL. 3 SHEETS-SHEET 2.

WITNESSES: mvemoR.

PATENTED NOV. 22, 1904.

M. PFATISGHER. VARIABLE SPEED MOTOR.

APPLICATION FILED APR. 7, 1904.

3 SHEETS-SHEET 3.

NOIMODEL.

FIG. V.

WITNESSES:

Patented November 22, 190

PATENT OFFICE,

MATHIAS PFATISCHER, OF PHILADELPHIA, PENNSYLVANIA.

VARIABLE-SPEED MOTOR.

SPECIFICATION forming part of Letters Patent N0 775,310, dated November22, 1904.

Application filed April '7, 1904:. Serial No. 202,070. (No modelfi Toall whom it may concern.-

Be it known that I, MATHIAs PFATISOHER, of Philadelphia, in the State ofPennsylvania, have invented certain new and useful 1mprovements inVariable-Speed Motors, whereof the following is a specification,reference being had to the accompanying drawings.

My improvements are particularly applicable to direct-currentshunt-wound motors; and it is an object of my invention to provide amotor of that type which will effect commutation without sparking with avariable load as well as at variable speed and which is capable ofrotation in either direction.

My present improvements may be more readily understood by firstreferring to certain conditions which are encountered in the operationof amotor of the class contemplated, as follows: When a brush-forinstance, of carbon-is in contact with two adjoiningcommutator-segments, the coil connected between said segments is shortcircuited on itself. The resistance of the short-circuited coil,together with the connections to the commutator, being very small ascompared with the contact resistance of the brush pressing on thecommutator, the strength of the currents flowing toward the brush fromthe respective commutator-segments will be dependent upon the relativevalue of the contact resistance, and the larger the latter the smallerWill be the currents. As the commutator rotates the contact-surfacebetween one segment and the brush becomes continually smaller, thecontact resistance increases, and the current flowing from that segmentto the brush becomes correspondingly smaller and finally reaches zero inValue, Whereas the reverse occurs at the adjoining segment, in which thecurrent gradually increases from zero to its maximum value.- The currentthus varying in the coil short-circuited between said segments generatesin the coil an electromotive force tending to maintain the said varyingcurrent, and it is this maintaining electromotive force which causessparking under the brushes under ordinary circumstances. Moreover, saidmaintaining electromotive force increases as the speed of rotatlonincreases, because the time for altering the current strength from plusto minus in said coil will be correspondingly less.

It is usual to minimize the aforesaid maintaining electromotive force bycausing the commutation (reversal of current in the shortcircuited coil)to take place in a weak magnetic field so constructed or arranged thatit produces in the short-circuited coil an electromotive force which isopposite in direction to said maintaining electromotive force andintended to be equal to it in value. Ordinarily it is possible to bringthe short-circuited armature-coils in such a compensating field byshifting the brushes, and if under such circumstances the armature speedincreases said compensating field generates an increased electromotiveforce which counterbalances the maintaining electromotive force, whichalso increases with the speed. However, in said ordinary method ofcommutation another disturbing condition arises from the fact that thearmature-coils, which carry the electric current, also react andgenerate a magnetic field whose influence is opposite to that which isnecessary to counteract the shortcircuited current, and accordinglyweakens said compensatory or commutation field. Moreover, such weakeningof the commutation-field is not of constant value, because it isdetermined by the armature-current, which varies with the load, so thatif the load becomes greater thearmature reaction increases, and with anincreased load a commutation field is produced which is insufficient toeffect the required compensation and sparking results.

In the specific case of a direct-current shuntwound motor having avariable speed an additional difliculty is encountered, because if themotor is to rotate at increased speed the strength of the main-fieldpoles must be decreased, and consequently with an increased number ofrevolutions the commutation-field will be weakened, the shortcircuitcurrent will not be reversed by the electromotiveforce designed tocorrect it, and the sparking at the brushes will be correspondinglyaugmented.

Of course if it is attempted to fit the motor to run in either directionby shifting the brushes to positions equidistant between the poles theyare removed from the aforesaid field of commutation and increasedsparking results.

The construction and arrangement contemplated by the present inventionprovides a motor which, with the brushes equidistant between the poles,is capable of reversing its direction of rotation without detriment, andeffects commutation in either direction of rotation without sparkingwith a variable load as well as at variable speed;

My improvements comprise the provision of auxiliary-field pole-pieceswhich are very small as compared with the main pole-pieces, which arelocated between the latter and provided with coils connected in serieswith the armature, so that all of the current taken by the latter flowsthrough the coils of said auxiliary field, which are so proportioned andarranged as to give the proper field for commutation. All of the coilsof said auxiliary field being connected in series with the armature,weakening of the field of commutation by an increased load is prevented,and said auxiliary poles produce the required compensatory field ofcommutation independently of the main field, which with increased numberof revolutions of the armature must be correspondingly weakened, asaforesaid. Moreover, the function or effect of the auxiliary poles isindependent of the direction of rotation of the armature, because if thelatter is reversed the current in the auxiliary field is also reversed.

My invention comprehends all of the novel features of construction andarrangement hereinafter more definitely specified.

Figure I is a diagrammatic view showing the wiring connections of amotor conven iently embodying my improvements. Fig. II is a wiringdiagram showing a modified arrangement of the field-coils with respectto the supply-mains. Fig. III is an end view of a motor-field frameparticularly adapted for the embodiment of this invention. Fig. IV is aside elevation of said field-frame, having a portion broken away to showthe peculiar diagonal relation of the field pole pieces. Fig. V is afragmentary plane development of the inner ends of the pole-pieces shownin perspective in Fig. IV.

Referring to Fig. I, the field-magnet frame 1 is provided with a seriesof four main-field pole-pieces 2 and a series of four auxiliaryfieldpole-pieces at, the members of the two series being alternately disposedin equidistant positions. The armature 10 is mounted to rotateconcentrically with respect to the two series of pole-pieces 2 and 4t,and the segments 12 of its commutator-ring are respectively connectedwith divisional coils of the armature. Said commutator is provided withcarbon brushes let and 15, and the former is connected by the lead 1'7with the supply-main 18. Said brush 15 is connected by the lead 20 withthe coils 22 of the auxiliary polepieces a, which, as indicated in Fig.l, are arranged in series relation and are of I'OSPOClLlYUl) alternatepolarity. The last coil 22 of said series is connected by the lead 24with the other supply-main The lead 27, connecting with the supply-main18, extends to the lever 28 of the rheostat, comprising thecontact-points 29 and variable-resistance coil 30, and the lead 32extends from said coil 30 to the coils 33 upon the main pole-pieces 2,which latter coils are connected in series relation with each other, butin shunt relation with the armature. The end coil $13 of said series isconnected by the leads 3% and 3:3 with the supply-main 25.

The direction of current through the armature and the consequentdirection of rotation of the latter may be reversed by any suitableswitch device-- for instance, that indicated at 36 in Fig. I.

The rheostat above described is a preferable means for manually varyingthe strength of the main field of the motor produced by the pole-pieces2 and their coils 33, it being noted, as aforesaid, that it is necessaryto weaken said field in correspondence with any desired increase in thenumber of revolutions of the armature. However, such regulation of saidfield may be effected by other 1neans----for instance, as shown in Fig.II, where the variable-resistance coil 37 is bridged across thesupply-mains 38 and 39 and provided with contact-points eiO, arranged tobe traversed by the lever 41. In the latter arrangement the mainfield-coils are in circuit between said lever 41 and the supply-main 38,as indicated at 42 in Fig. II.

The reversal of direction of the rotation of the armature as (shown inFig. Il) may be conveniently effected by the switch a l.

I find it advantageous to employ a fieldmagnet frame such as is shown inFigs. Ill and IV, wherein all of the pole-pieces 2 and a have theirfaces adjoining the armature disposed in diagonal relation to the axisof rotation of the armature, for the reason that such a construction andarrangement, although permitting ample gaps between the pole-pieces,produces a practically continuous magnetic field surrounding thearmature and insures a substantially uniform torque upon the latter. Asshown in said figures, the auxiliary polepieces 4 are embraced at theircentral portions by lugs 44, projectinginwardly from the frame 1, andare provided with foot-pads 9L5 for contact with the inner periphery ofsaid frame, to which they are independently secured by the bolts 17. Itmay be noted that the arrangement described facilitates the assembl ingof the auxiliary coils in proper position.

I do not desire to limit myself to the precise details of constructionand arrangement herein set forth, as it is obvious that various ICCmodifications may be made therein without departing from the essentialfeatures of my in- \ention.

I claim" 1. In a direct-current shunt-wound motor, the combination withan armature having a commutator; of a field-frame having a series offield poles; coils for said poles; connections including the coils ofalternate poles in said series in shunt relation to the armature;connections including other alternate coils in said series, in seriesrelation with the armature; current-supply connections to all of thecoils in said series; brushes in contact with said commutator; and,means arranged to adjustably vary the strength of the field in saidshunt-coils, independently of said series coils; whereby the armature isenabled to rotate at variable speed and variable load in eitherdirection without sparking and without variation in the position of thebrushes, substantially as set forth.

2. In a direct-current shunt-wound motor, the combination with anarmature having a commutator; of afield-frame having a series ofradially-disposed field pole-pieces; coils for said poles; connectionsincluding the coils of alternate poles in said series in shunt relationto the armature; connections including other alternate coils in saidseries, in series relation with the armature; current-supply connectionsto all of the coils in said series; brushes in contact with saidcommutator, in equidistant relation to adjoining poles in said series;and, means arranged to adjustably vary the strength of the field in saidshunt-coils, independently of said series coils; whereby the armature isenabled to rotate at variable speed and variable load in eitherdirection without sparking and without variation in the position of thebrushes, substantially as set forth.

3. In a direct-current shunt-wound motor, the combination with anarmature having a commutator; of a field-frame having a series offield-poles; having their faces adjoining the armature disposeddiagonally with respect to the armature-axis; coils for said poles;connections including the coils of alternate poles in said series inshunt relation to the armature; connections including other alternatecoils in said series, in series relation with the armature;current-supply connections to all of the coils in said series; brushesin contact with said commutator; and, means arranged to adjustably varythe strength of the field in said shunt-coils, independently of saidseries coils; whereby the armature is enabled to rotate at variablespeed and variable load in either direction without sparking and withoutvariation in the position of the brushes, substantially as set forth.

I. In a direct-current shunt-wound motor, the combination with anarmature having a commutator; of afield-frame having acircular series ofradially-disposed field pole-pieces,

having their faces adjoining the armature disposed diagonally withrespect to the armature-axis; coils for said poles; connectionsincludingthe coils of alternate poles in said series in shunt relation to thearmature; connections including other alternate coils in said series, inseries relation with the armature; current-supply connections common toall of the coils in said series; brushes in contact with saidcommutator, in equidistant relation to adjoining poles in said series;and, means arranged to adjustably vary the strength of the field in saidshunt-coils, independently of said series coils; whereby the armature isenabled to rotate at variable speed and variable load in eitherdirection without sparking and without variation in the position of thebrushes, substantially as set forth.

5. In a direct-current shunt-wound motor, the combination with anarmature having a commutator; of a field-frame; a circular series ofseparable field pole-pieces; means detachably securing said pole-piecesin said frame; coils for said poles; connections including the coils ofalternate poles in said series in shunt relation to the armature; connections including other alternate coils in said series, in series relationwith the armature; current-supply connections common to all of the coilsin said series; brushes in contact with said commutators; and, meansarranged to adjustabl y vary the strength of the field in saidshunt-coils, independently of said series coils; whereby the armature isenabled to ro tate at variable speed and variable load in eitherdirection without sparking and without variation in the position of thebrushes, substantially as set forth.

6. In a direct-current shunt-wound motor, the combination with anarmature having a commutator; of a field-frame; a circular series offield-poles, comprising two alternate series of pole-pieces ofrespectively different cross-sectional area; means detachably securingsaid pole-pieces in said frame; coils for said poles; connectionsincluding the coils of alternate poles in said series in shunt relationto the armature; connections including other alternate coils in saidseries, in series relation with the armature; current-supply connectionscommon to all of the coils in said series; brushes in contact with saidcommutator; and, means arranged to adjustably vary the strength of thefield in said shunt-coils, independently of said series coils; wherebythe armature is enabled to rotate at variable speed and variable load ineither direction without sparking and without variation in the positionof the brushes, substantially as set forth.

7. In a direct-current sh unt-wound motor, the combination with anarmature having a commutator; of a field-frame; a circular series offield-poles, comprising two alternate series of separable pole-pieces ofrespectively different cross-sectional area; means detachablysecuringsaid pole-pieces in said frame; coils for said poles;connections including the coils of alternate poles in said series inshunt relation to the armature; connections including other alternatecoils in said series, in series relation with the armature;current-supply connections common to all of the coils in said series;brushes in contact with said commutator, in equidistant relation toadjoining poles in said series; and, means arrai'iged to adjustably varythe strength of the field in said shunt-coils, independently of saidseries coils; whereby the armature is enabled to rotate at variablespeed and variable load in either direction Without sparking and withoutvariation in the position of the brushes, substantially as set forth.

8. In a direct-current shunt-wound motor, the combination with anarmature having a commutator; of a field-frame; a circular series offield-poles, comprising two alternate series of separable pole-pieces ofrespectively different cross-sectional area, having their facesadjoining the armature disposed diagonally with respect to thearmature-axis; means detachably securing said pole-pieces in said frame;coils for said poles; connections including the coils of alternate polesin said series in shunt relation to the armature; connections includ ingother alternate coils in said series, in series relation with thearmature; current-supply connections common to all of the coils in saidseries; brushes in contact with said commutator, in equidistant relationto adjoining poles in said series; and, means arranged to adjustablyvary the strength of the hold in said shuntcoils, independently of saidseries coils; whereby the armature is enabled to rotate at variablespeed and variable load in either direction Without sparking and withoutvariation in the position of the brushes, substantially as set forth.

In testimony whereof I have hereunto signed my name, at Philadelphia,Pennsylvania,this 6th day of April, 1904.

MATHIAS PFATLISCHER WVitnesses:

ARTHUR E. PAIGE, ANNA F. (Jrn'rzirnnm).

